Or just synthesize one your own. Sequences that code for virusses are available publicly, scientists have already created a virus from scratch a little over a year ago. A virus is basically a string of genetic material, packed in a coat. The coat is made by the host cell that reads the virus genetic material.

1. You can produce each part individually (genetic material, head, tail etc) and then assemble then using specific enzyme and solution. The protein part are usually clone and expresses in E. coli and the gentic material is clone and isolated from E. coli. RNA viruses are bit more complicated to produce.

2. If the virus needs a membrane coat then the virus is multiply on cell culture then isolate. Depending on what you require, you will use different type of cell. Bacteriaphage needs bacteria cell, whereas some only require epitlial cell from a bovine or human source. Chicken embryoe are use to make viral vaccine. The problem with this method, some viruses insert their genetic material inside their host genome. Therefore the production can stoped on its own.

If you need to do any modification to the virus you either isolated and clone the viral DNA. Do the modification and clone the DNA in a bacteria isolate the DNA and synthesised your viruse.

Now why would you want to create a synthetic virus? There are enough extant ones already and all synthetic ones so far (of the computer variety) have been nothing but trouble. It would seem that viruses mutate far too fast & unpredictably to be controllable for any beneficial purposes one may think of.

It's an interesting question. The viruses' genetic systems are very simple and we have been able to recreate them from scratch in the lab. The question arises whether we would be able to do the same for a cell. Also, the question arises whether it would be possible to create viruses unknown to science.

To do research. viruses are used as "delivery truck" for DNA. Modifying the virus ensure that some step will take place whereas other will. For example if you do not want the DNA to be integrate into the genome you remove the integrase. If you don't want the virus to lyse the cell you remove the gene that are necessary for the assembly and the structure. This technology migth also be used for genetic therapy.

Also to create vaccine. some viruses migth be used as the antigent presenting agent for other disease or be modified to create the desired immune responce.

Oh sure, about everything we do in science can be turned for the worse. Engineered virusses will hold great promise if they very selectively can target their load to specific cell types with high efficiency. Also, a virus can be made to which no cure exists of yet.

I have heard a saying once.. the last decades people have been working in labs trying to find cures for known diseases, now people are working in labs trying to create diseases for which no cure is known.